The United States and India began a high-level effort to conclude a controversial nuclear cooperation agreement that the State Department said was still within reach.

The United States and India on Tuesday began a high-level effort to conclude a controversial nuclear cooperation agreement that the State Department said was still within reach.

Hoping to end months of stalemate, top officials met in Washington for two days of talks on the deal, which would give New Delhi access to US nuclear fuel and reactors for the first time in 30 years.

"There are a couple of tough issues we have left to resolve. We believe we can get a deal, we can get an agreement," State Department spokesman Sean McCormack told reporters.

Indian officials said before the talks their government was expected to show little flexibility.

The slow pace appears to have delayed a possible visit by Indian Prime Manmohan Singh to US President George W Bush's Texas ranch, which had earlier been anticipated for this month.

Participants in the negotiations include Undersecretary of State Nicholas Burns, Indian National Security Adviser MK Narayanan and Indian Foreign Secretary Shiv Shankar Menon.

The Indian team is expected to meet at the White House on Wednesday with National Security Adviser Stephen Hadley.

Any deal must be approved by the US Congress. Support there for rapidly improving US-India ties is strong, but patience with what many see as India's unreasonable nuclear demands is waning.

"Either it's unacceptable (to India) and we should renegotiate it, or the Indians should accept this and we should pass it," a congressional aide said of the deal.

US congressional sources and other experts blame India's department of atomic energy for thwarting compromise and say Prime Minister Manmohan Singh is politically too weak to resist the nuclear establishment.

Key obstacles have included a US congressional mandate that Washington halt nuclear cooperation if India tests a nuclear weapon as it did in 1998.

Other disputed points have been the US refusal to give India prior approval to allow reprocessing of spent fuel with US components and to assure permanent fuel supplies. US law prohibits such assistance to countries such as India which are not formally recognized as nuclear powers.

A second congressional aide said he does not see a way to compromise on nuclear tests. A potential compromise floated by Indian press reports on the reprocessing issue also may be too difficult to work out, experts said.

The Bush administration considers the nuclear deal a major foreign policy success and is keen to have it take effect before Bush leaves office in January 2009.